S. R. Seshadri

Electromagnetic Gaussian beam

The governing equations for the paraxial approximation are deduced from Maxwell’s equations. The plane wave, in the paraxial approximation, is found to be transverse electromagnetic. For a field distribution at the input plane having a general azimuthal variation and a radial variation in the form of a Bessel function of an integer order with a Gaussian envelope of a given waist size, the spreading due to the Fresnel diffraction is determined as the paraxial beam is transported in the axial direction. The effects of Fresnel diffraction are illustrated with examples for a beam transporting unit power. Diffraction patterns of azimuthally symmetrical and dipolar modes are presented.

A multiple scattering interaction analysis of intersecting waveguides

A multiple scattering technique is developed for describing the physics of intersecting waveguides. In this picture the two waveguides interact by scattering the fields of each other in a self‐consistent manner. The development of such an analysis is motivated by the fact that the previous theory, which is based on the idea of symmetric and antisymmetric modes of the composite waveguide structure, has a limited validity. The analysis reveals new features of this geometry with important device applications in integrated optics.

Coupling of guided modes in thin films with surface corrugation

Two guided modes in a grounded, thin, dielectric film waveguide having a periodic corrugation of the interface between the film and the cover can interact selectively in the neighborhood of a particular frequency. Five different theories exist for the investigation of this interaction. The first three are small amplitude theories which assume that the amplitude of the corrugation relative to the thickness of the film is small and the third and the fourth theories are large amplitude theories which do not make such an assumption. In the small amplitude theories, solutions are sought as a perturbation of ideal normal modes and boundary conditions are applied on the average flat surface. The first small amplitude theory makes use of quasioptical considerations and the other two small amplitude theories employ wave‐theoretical techniques. All three theories lead to identical coupled mode equations governing the interaction. The first large amplitude theory is based on an expansion in terms of local normal mod...

Analysis of grating couplers in planar waveguides for waves at oblique incidence

A grating coupler is investigated for the case when the incident direction of a guided wave in a planar waveguide is inclined, within the guide plane, to the direction of a grating vector. The coupling and conversion between a TE, or TM, guided mode and the TE and TM radiative and nonradiative modes are considered in a weakly corrugated guide. The amplitude transport equation and the expressions for the leakage parameter, and the phase correction to a wave number of an unperturbed waveguide, are deduced using a quasi-optical technique. The power-conservation relation of a grating coupler for obliquely incident waves is established, and the coupling and conversion efficiencies are examined. It has been found that significant differences exist for excitation, or scattering, of waves at the normal and oblique incidences.

Experimental investigation of a thin‐film surface polariton polarizer

A new method of fabricating fiber optic surface polariton polarizers is described which produces devices with well‐defined lengths and fiber core to flat spacings. The results of experiments investigating the length dependence of the extinction ratio are interpreted through the use of a new theoretical analysis. Successful investigations of the dependence of the extinction ratio on the fiber core to flat spacing should be possible with further fabrication modifications.

Goos-Hänchen beam shift at total internal reflection

With reference to the treatment contained in a recent paper [ J. Opt. Soc. Am. A3, 550 ( 1986)], the regions of validity of the energy method of Renard for obtaining the Goos–Hanchen lateral shift are discussed, and the proper procedure for implementation of the energy method, including the interaction power flow introduced by Yasumoto and Ōishi [ J. Appl. Phys.54, 2170 ( 1983)], is described.

Thick metal surface-polariton polarizer for a planar optical waveguide

A metal half-space is situated parallel to a planar dielectric film waveguide. As a consequence of the wave interaction between the surface polariton supported by the metal surface and the transverse-magnetic guided mode of the dielectric film, either the latter can be completely extinguished or its power can be substantially reduced in a small interaction length. The insertion loss in the same interaction length for the transverse-electric guided mode of the dielectric film is negligibly small. A metal cladding therefore serves as a polarizer for a planar dielectric film waveguide. The theory of this surface-polariton polarizer for a planar dielectric film optical waveguide is developed, and representative numerical results are presented.

Analysis of grating couplers for planar dielectric waveguides

Output and input grating couplers for step index planar dielectric waveguides are investigated taking into account the interaction between a guided mode with a finite number of radiative and an infinite number of nonradiative space harmonics. For transverse electric and transverse magnetic modes, and for shallow gratings of arbitrary profiles located at either the upper or the lower guide surface, the governing equation for the slowly varying amplitude of the guided wave is deduced, and therefrom the real and the imaginary parts of the correction to the wave number of unperturbed guide are evaluated, the power conservation relation is established, and the output and the input coupling efficiencies are defined. For the input coupler, the excitation by a two‐dimensional radiation beam is also included. The role of the space harmonics which, like the guided wave, carry power along the guide in modifying the real and the imaginary parts of the wave number of the guided wave is discussed. The effect of the cho...

Excitation and scattering of guided modes on a dielectric cylinder with a periodically varying radius

The excitation and scattering of guided modes on a cylindrical dielectric waveguide with a corrugated surface is investigated. The interactions between the finite number of radiation modes and an infinite number of surface modes are considered with the consequence that both the amplitude and phase of the interacting modes are evaluated. The excitation by a two‐dimensional beam is analyzed and the transverse electric and transverse magnetic modes are investigated. The power conservation relation of a corrugated cylinder is established and the reciprocity relations are investigated in general terms starting from the principle of time reversal. The fields of a finite length corrugated cylinder are used to obtain the far‐field radiation pattern and treat its frequency characteristics. The effects of dielectric permittivity, dielectric losses, dephasing measure, and the grating profile are investigated.

Leaky surface polariton

The characteristics of a leaky surface polariton existing on the surface of a free electron metal having the profile of an ordinary diffraction grating are investigated including the effects of the finite length of the grating and the slow spatial variation of the amplitude of the surface polariton. The radiative decay characteristics of the surface polariton and the characteristics of the antiresonance in the angular response of the reflectivity of light incident on the grating are discussed, and the effect of a small dissipation in the metal on these characteristics is also included.